This application is related to Japanese Patent Application No. 2000-059268 filed on Mar. 3, 2000, whose priority is claimed under 35 USC xc2xa7119, the disclosure of which is incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a GALVANO-micromirror, particularly a GALVANO-micromirror of an electrostatic actuation type to be used to control a position irradiated by a light beam in an optical disk driving device, and its manufacture process.
2. Description of Related Art
A currently available usual GALVANO-micromirror of the electrostatic actuation type is disclosed, for example, by Silicon Torsional Scanning Mirror (IBM J.RES. and DEVELOP., Vol. 24, No. 5, September 1980. This GALVANO-micromirror is provided with an electrode substrate 100 and a mirror substrate 102 situated thereon, as shown in FIGS. 16 and 17.
The mirror substrate 102 includes a frame-form base 104, a mirror section 106 having a mirror face 106a formed on one main surface thereof, torsion bar sections 108 connecting the base section 104 to the mirror section 106 and supporting the mirror section 106 pivotally. On the other main surface of the mirror section 106, there is formed a first electrode composed of a pair of electrode plates 110a and 110b. On the electrode substrate 100, there is formed a second electrode composed of a pair of electrode plates 112a and 12b opposing the electrode plates 110a and 110b of the first electrode. On the electrode substrate 100, a linear projection 100a is integrally formed which abuts the mirror section 106 and has a mountain-like cross section. The ridge of the projection 100a extends along the axis of the torsion bar sections 108.
In this GALVANO-micromirror, when voltage is applied across one electrode plate 110a of the first electrode and one electrode plate 112a of the second electrode, the mirror section 106 pivots by electrostatic attraction in an anti-clockwise direction in FIG. 17. When voltage is applied across the other electrode plate 110b of the first electrode and the other electrode plate 112b of the second electrode, the mirror section 106 pivots by electrostatic attraction in a clockwise direction in FIG. 17. Since such electrostatic attraction is proportional to the area of the electrodes, the first electrode comprised of the electrode plates 110a and 110b is formed almost all over the other main surface of the mirror section 106, for allowing actuation by a lower voltage. The size of the electrode plates 112a and 112b of the second electrode is determined according to the size of the electrode plates 110a and 110b of the first electrode.
A GALVANO-micromirror used in an optical disk driving device is disclosed by Japanese Unexamined Patent Publication No. HEI 9(1997)-146034. This GALVANO-micromirror also has the function of oscillating a mirror substrate by electrostatic attraction between an electrode mounted on the mirror substrate and an electrode mounted on the surface of an electrode substrate opposedly to the electrode on the mirror substrate when voltage is applied across the electrodes, like the GALVANO-micromirror shown in FIG. 16.
Micromirrors used in optical disk driving devices are required to have high-performance electric-mechanic operation characteristics and also required in particular to have an excellent flatness and a reduced size in outward form for thinning the optical disk driving devices. For example, a flatness of 0.05xcex (xcex is wavelength of a light source used) is demanded. For size reduction, the length in a direction defined by linking two torsion bars (a longitudinal direction in FIG. 16) needs to be shortened.
Japanese Unexamined Patent Publication No. HEI 7(1995)-287177 discloses a micromirror in which a torsion bar is mounted under a mirror. This structure is formed using a so-called surface micromachining technique by which thin films are laminated on a substrate while being patterned in desired configuration sequentially by utilizing formation, patterning and removal of sacrificial layers.
However, the current surface micromachining technique can form thin-film mirror structures of several micrometers or more thickness. If a mirror face having a flatness acceptable for the optical disk driving devices is intended to be realized, it is only possible to produce a mirror face of about several hundreds of micrometers in size at the largest.
Generally, the micromirrors used for optical disk driving devices are in the shape of a square or an ellipse of several millimeters and have a primary resonant frequency as low as about 100 to several hundreds Hz. If a micromirror of such size is produced by the surface micromachining technique, there occur curves and distortions in the resulting thin film because of residual stress generated during the production process. Also since the micromirror is a thin-film mirror, distortions occur during operation and the mirror face cannot have a required flatness.
For example, for maintaining a necessary optical flatness sufficiently high with a mirror face of several millimeters square having a metal film of high reflectance or a multi-layered film of dielectric, it is presumed by experience that the thickness of the mirror needs to be about 150 xcexcm at the minimum. Therefore, it is hard to produce a micromirror having a low resonance frequency and a high flatness which can be used for optical disk devices, by the surface micromachining technique using the step of laminating thin films and sacrificial films.
The present invention provides a GALVANO-micromirror and its production process which realize a miniaturized micromirror having sufficient performance for being used for optical disk driving devices.
The present invention provides a GALVANO-micromirror including a first substrate having a light-reflective mirror face on one surface thereof and a first electrode on one or both surface(s) thereof; and a second substrate including a frame-form base, a second electrode located opposedly to the first electrode, a joint holder section located under the mirror face for holding the first substrate, and a torsion bar section located under the mirror face for connecting the frame-form base to the joint holder section and supporting the joint holder section pivotally within a range of angles, wherein a part of a surface of the first substrate on which the mirror face is not formed is joined to the joint holder section of the second substrate.
With this construction, the GALVANO-micromirror can be reduced in size while maintaining performance required for being used in optical disk driving devices.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.